1. Field of the Invention
Preferred embodiments relate to an apparatus and method for making multi-layer polyesters, preferably comprising virgin polyethylene terephthalate (PET), recycled polyethylene terephthalate (RPET) or post-consumer recycled polyethylene terephthalate (PCR PET), a barrier layer and articles made therefrom. Preferably the multi-layer polyester takes the form of preforms having a barrier layer internally applied to the bottles blow-molded therefrom.
2. Description of the Related Art
The use of plastic containers as a replacement for glass or metal containers in the packaging of beverages has become increasingly popular. The advantages of plastic packaging include lighter weight, decreased breakage as compared to glass, and potentially lower costs. The most common plastic used in making beverage containers today is PET. Virgin PET has been approved by the FDA for use in contact with foodstuffs. Containers made of PET are transparent, thin-walled, lightweight, and have the ability to maintain their shape by withstanding the force exerted on the walls of the container by pressurized contents, such as carbonated beverages. PET resins are also fairly inexpensive and easy to process.
However, the use of strictly virgin materials in the production of plastic containers raises environmental concerns. Both public and governmental pressures have been placed on manufacturers using and producing plastic containers to incorporate post-consumer recycled plastics into their packaging. Additionally, recycled resins are less expensive than their virgin counterparts. Therefore, it is desirable to utilize recycled PET in the production of containers currently being manufactured entirely from virgin PET.
At least two issues have prevented the widespread incorporation of recycled PET in the beverage container industry. First, PET is a naturally crystalline material, that is, if allowed to cool slowly, will orient itself into an organized, crystalline structure. A crystalline structure inhibits the creation of a strong interface between the virgin material and the recycled material, and inhibits blow molding, which can prevent the resulting bottle from being clear and structurally functional.
Secondly, since pet containers can be manufactured by injection molding using only a single injection of PET, manufacture is relatively easy and production cycle time is low. Thus, PET containers are inexpensive. Even if post-consumer recycled PET materials can be bonded to virgin PET to create a saleable container, methods and apparatus for making such containers within a competitive cycle time and cost have not been devised. Production cycle time is especially important because a lower cycle time enables a manufacturer to make more efficient use of its capital equipment. Specifically, a low cycle time enables higher volume and less expensive production of containers.
For a container incorporating recycled material to be commercially feasible, increased costs associated with any increase in cycle time necessary to incorporate the recycled material must be offset by increased content of the recycled material relative to the total material of the container. The additional recycled material replaces a similar amount of virgin material and is less expensive, therefore recovering at least a portion of the costs of slower production. Current techniques limit recycled content to about 10%, which is generally not enough to recoup the costs of increased cycle time. It is desirable to incorporate at least 25%-50% recycled material to in order to at least “break even” in terms of any increase in cycle time. It is also desirable to minimize cycle time increases associated with incorporating recycled material. Therefore, a need exists for a relatively low cycle time and a high recycled material content production method and apparatus to provide a viable alternative to monolayer, virgin PET containers.
Further, assuming an acceptable PET/PCR PET container can be produced within a reasonable cycle time, there is an additional downside to the use of PET in thin-walled beverage containers: permeability to gases such as carbon dioxide and oxygen. The permeability of PET bottles results in soft drinks that go “flat” due to the egress of carbon dioxide, as well as beverages that have their flavor spoiled due to the ingress of oxygen. Thus, it would also be preferable to provide gas barrier protection to the PET/PCR PET preform or container.
However, existing multi-layer preforms and containers are not compatible with the processes employed to add a barrier layer. For example, a preform to which a barrier layer is added is likely to delaminate upon blow-molding. Similarly, existing multi-layer containers suffer from warping and/or delamination due to the heat or vacuum conditions associated with typical barrier coating processes.
In addition, as mentioned previously, an amorphous or semi-crystalline state is preferred to allow for blow molding of the PET preform, with or without recycled content. However, such bottles may not have enough dimensional stability to withstand a hot-fill process due to the relatively low Tg of the PET material and the tight tolerances required when using standard threaded closures. In these circumstances, a bottle made of semi-crystalline or crystalline PET would be preferred, as it would hold its shape during warm-fill and hot-fill processes.
Thus, the need exists for an apparatus and method for making recycled material content PET preforms and containers which are economical, cosmetically appealing, and have good barrier and physical properties, and are able to maintain dimensional stability during a hot-fill process remains unfulfilled.